The reflexive Banach space fixed point property conjecture
Let be a Banach space. It has the fixed point property for nonexpansive mappings when every nonempty closed, convex and bounded subset and every map satisfying
for all has a fixed point in .
Reflexive-space fixed point conjecture. Every reflexive Banach space has the fixed point property for nonexpansive maps. Equivalently, if is reflexive and is closed, bounded and convex, then every nonexpansive self-map has a fixed point.
Reflexivity guarantees weak compactness of bounded subsets, but known fixed point theorems generally require additional hypotheses such as uniform convexity or normal structure. Nonreflexive examples exist both with and without the property, while the existence of a reflexive Banach space failing the fixed point property remains open.
References
Primary source
Faruk Alpay and Hamdi Alakkad, “On the Fixed Point Property in Reflexive Banach Spaces”, arXiv:2509.13121 (2025).
Progress summary
Nothing recorded yet. Refresh searches the literature and the public web for attempts on this problem, and writes the first summary here.
Solutions 1
RemarkAI-assistedClaimed by OpenAI. Claims the fixed-point property in the given norm for every real reflexive Banach space: every nonexpansive selfmap of a nonempty closed bounded convex subset has a fixed point.See full solution
Claimed by OpenAI. Claims the fixed-point property in the given norm for every real reflexive Banach space: every nonexpansive selfmap of a nonempty closed bounded convex subset has a fixed point.
Scope relative to this problem: The source claims the fixed-point property in the given norm of every real reflexive Banach space, for nonexpansive selfmaps of every nonempty closed bounded convex subset. This retains the source real-scalar convention and does not change the assertion to existence of an equivalent norm or to group-action fixed-point properties.
GitHub repository: https://github.com/openai/math
- OpenAI-328-01-Fixed-Points-of-Nonexpansive-Maps-in-Reflexive-Banach-Spaces.pdfOpen